It's time to stop pussyfooting around. Double the length of the runway at Belfast City Airport, then reclaim Victoria Park, the land north of the runway and as much of Belfast Lough as needed for aircraft parking, hangars and a freight complex.
Using Gatwick as a model, develop Sydenham station as the rail hub for the city, build a new airport terminal over it with a heliport on the roof.
Close Aldergrove. It's not required by the military and too far out in the 'sticks' to be of use to anyone. Move all aircraft and flights to the city and have no restriction on movements and passenger numbers.
Finally, rename it 'The Pride of Belfast Best City Airport in the World'!